The term “biodiversity” refers to the variety of life forms in a habitat, whether it’s a local environment or an entire planet. Most of the species making up our planetary biodiversity are still poorly studied or completely unknown; experts estimate that there may be at least four times as many complex (eukaryotic) species alive on our planet as the 1.9 million that have already been discovered and named, possibly more. Even as we are becoming aware of the massive biodiversity of Earth, we are also in the midst of a biodiversity crisis, with species going extinct at rates rivaling those of the major mass extinctions of Earth’s history. Therefore, while the definition of the term “biodiversity” is simple, it in fact encompasses some of humanity’s (and science’s) biggest challenges.
There are a number of reasons why understanding and preserving biological diversity is important. Above all, every species is unique in its combination of evolutionary history and ecological role, so taken together they are a global resource—like a library preserving the heritage of life itself.
The continuation of life as a whole is dependent on the presence of a variety of different species able to perform a variety of roles under a variety of circumstances. In the first chapter of his classic work on biodiversity, The Diversity of Life, entomologist Edward O. Wilson describes a violent thunderstorm in the Brazilian rainforest and the way the forest revives itself after suffering physical damage—a process that can occur because a diversity of species is present to capably adapt to the damage and rebuild the environment.
This function of biodiversity is also relevant in manmade systems, such as agriculture. When we depend on only one or a few types of crops, our food supply becomes vulnerable to disease, infestation, and extreme weather. A famous example of the danger of low agricultural biodiversity is the Irish potato famine of 1845, during which the single potato species that the population consumed was effectively wiped out by the late blight fungus. Environmental thinkers from Aldo Leopold to Michael Pollan have recognized the importance of biological diversity as insurance against famine. The more species that are available, the more likely it is that there will be some adapted to handle some new threat, disturbance, or human need.
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